This application is based on Japanese Patent Application No. 2001-362656 filed on Nov. 28, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a combustion detecting apparatus of an engine for determining a combustion condition of the engine based on ion current.
2. Description of Related Art
Conventionally, in order to detect a combustion condition of an engine, there has been developed a technology of detecting ion current flowing in an electrode of an spark plug at each ignition and determining firing/misfire or the like based on an ion current detecting signal thereof.
Further, as a combustion detecting apparatus of an engine using a technology of this kind, according to, for example, JP-A-11-13616, there is described an apparatus in which an ion current detecting signal is inputted to a filter for passing only a signal equal to or larger than a predetermined threshold and having a width equal to or larger than a predetermined time period, an output signal of the filter is inputted to a peak hold circuit, an output of the peak hold circuit is subjected to A/D conversion at a predetermined timing after ignition (for example, timing of ATDC60xc2x0 CA), when the A/D conversion value (that is, a peak hold value of the output signal of the filter by the peak hold circuit) is equal to or larger than a determining reference value, a firing is determined, otherwise, a misfire is determined.
However, there poses the following problem according to the apparatus described in the publication.
That is, the peak hold circuit is constructed by a constitution of storing electric charge in a capacitor and therefore, when peak hold time is long, by leak current of the circuit or discharging the electric charge of the capacitor, peak hold voltage is lowered and a correct peak hold value is not provided. Particularly, when the output of the peak hold circuit is subjected to A/D conversion at a timing of a specific crank angle after ignition (ATDC60xc2x0 CA in the above-described example), in accordance with rotational speed (rotational number) of the engine, the lower the rotational number, the longer the time period from ignition to the timing of the specific crank angle and therefore, the peak hold voltage is liable to lower. Therefore, the apparatus is disadvantageous in accurately determining the combustion condition of the engine.
Hence, it is conceivable to construct a constitution as shown by FIG. 16 without using an analog peak hold circuit.
That is, first, the ion current detecting signal is inputted to a low pass filter 101 and an output signal of the low pass filter 101 is subjected to A/D conversion at every constant time period by an A/D converter 103. Further, it is conceivable to adopt a constitution in which CPU 105 carries out a peak hold processing of calculating a maximum value (peak value) of an A/D conversion value at the every constant time period by the A/D converter 103, compares a maximum value provided in the peak hold processing with a predetermined determinant (threshold) Vth, determines a firing when the maximum value is larger and determines a misfire otherwise.
However, in the case of the constitution, as exemplified in FIG. 17, (b), (c), and (d), there is a case in which a period of generating noise in the ion current detecting signal and an A/D conversion timing by the A/D converter 103 are synchronized. In this case, a signal of the noise is erroneously determined as a signal indicating a firing. That is, even in the case of a misfire, the misfire is erroneously determined as a firing. Further, in FIG. 17, (b), (c) and (d), the A/D conversion timing is indicated by a black circle mark (xe2x97xaf). In FIG. 17, (b) shows normal combustion. In FIG. 17, (c) shows the case of a misfire. In FIG. 17, (d) shows a case of increasing the time constant of the low pass filter. In FIG. 17, (a) shows an ignition signal and time t0 is the ignition timing.
Therefore, although it is conceivable to construct a constitution of setting an A/D conversion period (time interval of A/D conversion) to be short and determining whether a noise signal is constituted from a state of changing each A/D conversion value, there is needed an A/D converter capable of carrying out high-speed A/D conversion or CPU capable of carrying out high-speed processing, which results in a significant increase in cost.
Further, although it is also conceivable to enhance a filter effect (voltage smoothing effect) of the low pass filter 101, thereby, as exemplified in (d) of FIG. 17, an original waveform of the ion current detecting signal is significantly blunted, an accurate peak hold value is not provided and therefore, the combustion condition cannot accurately be determined.
Meanwhile, the above-described respective problem is not limited to the constitution of subjecting the ion current detecting signal to peak holding but is similarly posed also in the case of, for example, an integrating constitution. That is, in the apparatus described in the publication, even in the case of providing an integrating circuit in place of the peak hold circuit and determining firing/misfire based on an output of the integrating circuit, the integrating circuit is constructed by a constitution of storing electric charge in a capacitor and therefore, when an integrating time period is long, output voltage in correspondence with an integrated value is lowered and a correct integrated value is not provided. Further, in the constitution of FIG. 16, even in a case in which CPU 105 carries out an integrating processing for calculating an integrated value of the A/D conversion value at every constant time period and determining firing/misfire based on the integrated value provided by the processing, the problems described in reference to FIG. 17, (b), (c) and (d) are similarly posed.
The invention has been carried out in view of the problems and it is an object thereof to provide a combustion detecting apparatus capable of accurately determining a combustion condition of an engine from an ion current detecting signal without shortening an A/D conversion period for excluding influence of noise.
According to an aspect of the invention, ion current detecting means detects an ion current flowing in electrodes of a spark plug of the engine and outputs an ion current detecting signal of a voltage in accordance with the ion current. Further, A/D conversion means subjects the ion current detecting signal outputted from the ion current detecting means at every predetermined time period to A/D conversion and A/D conversion value storing means stores an A/D conversion value by the A/D conversion means.
Further, reference voltage producing means produces a reference voltage large or small of which is compared with the ion current detecting signal and voltage change storing means stores that the ion current detecting signal traverses the reference voltage by comparing the ion current detecting signal and the reference voltage.
Further, at every timing of subjecting the ion current detecting signal to A/D conversion by the A/D conversion means (A/D conversion timing), erasing means determines whether the ion current detecting signal is stored to traverse the reference voltage in the voltage change storing means, erasing a stored value of the A/D conversion value storing means prior to an A/D conversion timing at a current time and erasing a memory of the voltage change storing means when the ion current detecting signal is stored to traverse the reference voltage. Further, combustion condition determining means determines a combustion condition of the engine based on the stored value of the A/D conversion value storing means which has not been erased continuously over A/D conversion timings more than a predetermined number of times M by the erasing means.
Further, when the traversing of the reference voltage by the ion current detecting signal is defined as xe2x80x9ctraversing of the ion current detecting signalxe2x80x9d or simply as xe2x80x9ctraversingxe2x80x9d, as the traversing, there are traversing in a first direction for traversing the reference voltage by the ion current detecting signal in a direction from a voltage side which does not indicate a firing to a voltage side which indicates a firing relative to the reference voltage and traversing in a second direction for traversing the reference voltage by the ion current detecting signal in a direction from a voltage side which indicates a firing to a voltage side which does not indicate a firing relative to the reference voltage and traversing of the ion current detecting signal constituting a storage object by the voltage change storing means, may be both of traversing in the first direction and traversing in the second direction or may be either one thereof.
A/D conversion value at every predetermined time period of the ion current detecting signal is stored by the A/D conversion value storing means. When there is produced traversing of the ion current detecting signal constituting the storage object by the voltage change storing means, at an A/D conversion timing immediately thereafter, a stored value of the A/D conversion value storing means therebefore is erased by the erasing means. Further, according to the combustion detecting apparatus, the combustion condition of the engine is determined based on the stored value of the A/D conversion value storing means which has not been erased continuously over A/D conversion timings more than a predetermined number of times M by the erasing means.
Therefore, when there is produced traversing of the ion current detecting signal constituting the storage object by the voltage change storing means during a time period in which A/D conversion of the ion current detecting signal is executed at least by xe2x80x9cM+1xe2x80x9d times, the A/D conversion value at the A/D conversion timing until that time is not used for determining the combustion condition of the engine. Further, in the case in which there is not produced traversing of the ion current detecting signal constituting the storage object by the voltage change storing means during A/D conversion timings larger than M times, the combustion condition of the engine is determined from the A/D conversion value during the time period.
According to the combustion detecting apparatus, even when there is produced noise having a period equal to or smaller than an A/D conversion period in the ion current detecting signal, an A/D conversion value of the noise is not used for determining the combustion condition. An erroneous determination can be prevented without shortening the A/D conversion period, the A/D conversion period can be set to be long and therefore, processing load of A/D conversion and for storing the A/D conversion value can be alleviated.
According to another aspect of the invention, similar to the combustion detecting apparatus according to the first aspect, the ion current detecting means detects the ion current flowing in the electrodes of the spark plug of the engine and outputs the ion current detecting signal of the voltage in accordance with the ion current and the A/D conversion means subjects the ion current detecting signal outputted from the ion current detecting means to A/D conversion at every predetermined time period. Further, the reference voltage producing means produces the reference voltage the large or small of which is compared with the ion current detecting signal.
Voltage change informing means informs that the ion current detecting signal traverses the reference voltage in a first direction constituting a direction from a voltage side which does not indicate a firing to a voltage side which indicates a firing relative to the reference voltage (traversing in the first direction) and that the ion current detecting signal traverses the reference voltage in a second direction constituting a direction from the voltage side which indicates a firing to the voltage side which does not indicate a firing relative to the reference voltage (traversing in the second direction) by comparing the ion current detecting signal and the reference voltage.
Further, A/D conversion value storing means stores an A/D conversion value by the A/D conversion means during a time period from informing traversing in the first direction to informing traversing in the second direction by the voltage change informing means.
Further, determining means determines whether a number of times of A/D conversion by the A/D conversion means from informing traversing in the first direction to informing traversing in the second direction by the voltage change informing means, is larger than a predetermined number of times N.
Further, combustion condition determining means determines the combustion condition of the engine based on a stored value of the A/D conversion value storing means when it is determined that the number of times of A/D conversion is larger than the predetermined number of times N by the determining means.
When the ion current detecting signal traverses the reference voltage in the second direction until A/D conversion of the ion current detecting signal is executed at least by xe2x80x9cN+1xe2x80x9d times since the ion current detecting signal traverses the reference voltage in the first direction, the A/D conversion value at the A/D conversion timing until that time, is not used for determining the combustion condition of the engine. Further, when there are present A/D conversion timings more than N times during a time period of traversing the reference voltage in the first direction to traversing the reference voltage in the second direction by the ion current detecting signal, the combustion condition of the engine is determined from the A/D conversion value during the time period.
Therefore, also by the combustion detecting apparatus, even when there is produced noise having a period equal to or smaller than the A/D conversion period in the ion current detecting signal, signal of the noise is not erroneously determined to be a signal indicating a firing. Further, the erroneous determination can be prevented without shortening the A/D conversion period, the A/D conversion period can be set to be long and therefore, the processing load of A/D conversion and for storing the A/D conversion value can be alleviated.
The A/D conversion means, the A/D conversion value storing means and the determining means may be operated only in a detecting window suitable for determining the combustion condition of the engine.
It is preferable to set the detecting window to start from a predetermined timing after an ignition timing (for example, a timing at which a predetermined time period has elapsed from the ignition timing or a timing of a predetermined crank angle after the ignition timing). This is because generally, in ignition, there is produced a noise having a narrow width by LC resonance of an ignition coil and thereafter, the ion current by a firing is produced and a time period of producing such a noise can effectively be avoided.
The A/D conversion value storing means may be constituted to detect a maximum value of the A/D conversion value by the A/D conversion means and store the maximum value. That is, although the A/D conversion value storing means can be constituted to successively store the A/D conversion value per se by the A/D conversion means, memory capacity can be reduced by executing peak hold processing of updating and storing only the maximum value of each A/D conversion value.
The A/D conversion value storing means may be constructed a constitution in which the A/D conversion value by the A/D conversion means is integrated and an integrated value thereof is stored.
The combustion condition determining means may be constituted to compare a determinant which is larger in a direction of indicating a firing than a tolerance range in designing the reference voltage generated by the reference voltage generating means and a determinant set in accordance with a state of operating the engine, and a stored value of the A/D conversion value storing means to thereby determine the combustion condition of the engine.
In finally determining the combustion condition of the engine, there is used the determinant set in accordance with the state of operating the engine and therefore, the combustion condition of the engine can be accurately determined. Further, accuracy of the reference voltage produced by the reference voltage producing means may be low and therefore, low cost formation of the reference voltage producing means can be achieved.